Method for installation of artificial hemi-lumbar interbody spinal fusion implant having an asymmetrical leading end

ABSTRACT

An artificial interbody spinal implant adapted for placement across an intervertebral space formed across the height of a disc space between two adjacent vertebral bodies is disclosed. The implant has an asymmetrical leading end adapted to sit upon the more peripheral areas, such as the apophyseal rim and the apophyseal rim area, of the vertebral end plate region of the vertebral bodies without protruding therefrom. The asymmetrical leading end allows for the safe use of an implant of maximum length for the implantation space into which it is installed. The implant can also include an asymmetric trailing end adapted to sit upon the more peripheral areas of the vertebral end plate region of the vertebral bodies.

This application is a divisional of application Ser. No. 09/553,573,filed Apr. 19, 2000, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to interbody spinal implantspreferably adapted for placement in pairs side by side to either side ofthe midline with or without a space therebetween into a space createdacross the height of a disc space and between two adjacent vertebralbodies, after the removal of damaged spinal disc material, for thepurpose of correcting spinal disease at that interspace. The spinalimplants are made of an implant material that is other than bone and mayor may not be resorbable. Where the implants are spinal fusion implants,they are adapted such that fusion occurs at least in part through theimplants themselves. Where the implants are motion preserving formaintaining spinal motion, bone growth can occur at least in part intothe spinal implants themselves, but not across them, and they areadapted to allow for relative motion between the vertebrae.

2. Description of the Related Art

Surgical interbody spinal fusion generally refers to the methods forachieving a bridge of bone tissue in continuity between adjacentvertebral bodies and across the disc space to thereby substantiallyeliminate relative motion between the adjacent vertebral bodies. Theterm “disc space” refers to the space between adjacent vertebral bodiesnormally occupied by a spinal disc.

Motion preserving implants maintain the spacing between the two adjacentvertebral bodies and allow for relative motion between the vertebrae.Bone growth from the adjacent vertebral bodies into the motionpreserving implant, but not through the implant, anchors the implant tothe adjacent vertebral bodies while preserving the relative motionbetween the vertebrae.

Spinal implants can have opposed upper and lower surfaces that arearcuate or non-arcuate transverse to the longitudinal axis of theimplant along at least a portion of the length of the implant. Implantshaving arcuate opposed portions are adapted to be implanted across andbeyond the height of the restored disc space, generally into a boreformed across the height of a disc space. Some of the advantages offeredby implants with arcuate opposed portions include: 1) the installationof the implant into vascular bone made possible by the creation of abore into the bone of the adjacent vertebral bodies; 2) the implant'sgeometric shape is easy to manufacturer; 3) the implant can includeexternal threads to facilitate insertion into the implantation space;and 4) the implant provides more surface area to contact the adjacentvertebral bodies than would a flat surface. Some disadvantagesassociated with implants having arcuate opposed portions include: 1) thecreation of a bore into the adjacent vertebral bodies to form theimplantation space results in a loss of the best structural bone of thevertebral endplate; 2) the implant needs to have a larger cross sectionto fill the prepared implantation site which may be more difficult toinstall, especially from a posterior approach; and 3) the width of theimplant is generally related to the height of the implant, so if theimplant is for example a cylinder, the width of the implant may be alimiting factor as to the height of the implant and therefore to thepossible usefulness of the implant.

Implants having non-arcuate upper and lower opposed portions may beimpacted into a space resembling the restored disc space and need onlybe placed against a “decorticated endplate.” A decorticated endplate isprepared by the surgeon to provide access to the underlying vascularbone. Some of the advantages provided by implants having non-arcuateopposed portions include: 1) preserving the best bone in the endplateregion; 2) the height of the implant is independent of its width; 3) theimplant can be of a geometric shape and the opposed upper and lowersurfaces can be flat; 4) the implants can be installed as part of amodular unit; and 5) the implants can provide a broad surface contact.Some of the disadvantages provided by implants having non-arcuateopposed portions include: 1) the implants cannot be threaded in and mustbe impacted into the installation space; and 2) the recipient site maybe more difficult to prepare.

Human vertebral bodies have a hard outer shell of compacted densecancellous bone (sometimes referred to as the cortex) and a relativelysofter, inner mass of cancellous bone. Just below the cortex adjacentthe disc is a region of bone referred to herein as the “subchondralzone”. The outer shell of compact bone (the boney endplate) adjacent tothe spinal disc and the underlying subchondral zone are together hereinreferred to as the boney “end plate region” and, for the purposes ofthis application, is hereby so defined. A circumferential ring of densebone extends around the perimeter of the endplate region and is themature boney successor of the “apophyseal growth ring”. Thiscircumferential ring is formed of very dense bone and for the purposesof this application will be referred to as the “apophyseal rim”. For thepurposes of this application, the “apophyseal rim area” includes theapophyseal rim and additionally includes the dense bone immediatelyadjacent thereto. The spinal disc that normally resides between theadjacent vertebral bodies maintains the spacing between those vertebralbodies and, in a healthy spine, allows for the normal relative motionbetween the vertebral bodies.

FIG. 1 of the attached drawings shows a cross-sectional top plan view ofa vertebral body V in the lumbar spine to illustrate the dense bone ofthe apophyseal rim AR present proximate the perimeter of the vertebralbody V about the endplate region and an inner mass of cancellous boneCB. The structure of the vertebral body has been compared to a core ofwet balsa wood encased in a laminate of white oak. The apophyseal rim ARis the best structural bone and is peripherally disposed in the endplateof the vertebral body.

FIG. 2 is a top plan view of a fourth level lumbar vertebral body Vshown in relationship anteriorly with the aorta and vena cava(collectively referred to as the “great vessels” GV). FIG. 3 is a topplan view of a first sacral level vertebral body V shown in relationshipanteriorly with the iliac arteries and veins referred to by thedesignation “IA-V”. Because of the location of these fragile bloodvessels along the anterior aspects of the lumbar vertebrae, no hardwareshould protrude from between the vertebral bodies and into the greatvessels GV and iliac arteries and veins IA-V.

Implants for use in human spinal surgery can be made of a variety ofmaterials not naturally found in the human body. Such materials includesurgical quality metals, ceramics, plastics and plastic composites, andother such materials suitable for the intended purpose. Further, thesematerials may be absorbable, bioactive such as an osteogenic material,or be adapted to deliver and/or contain fusion promoting substances suchas any of bone morphogenetic protein, hydroxyapatite, and genes codingfor the production of bone, and/or others. Fusion implants preferablyhave a structure designed to promote fusion of the adjacent vertebralbodies by allowing for the growth of bone through the implant fromvertebral body to adjacent vertebral body. This type of implant isintended to remain indefinitely within the patient's spine unless madeof a resorbable or bioresorbable material such as bone that can bebiologically replaced in the body over time such that it need not beremoved as it is replaced over time and will no longer be there.Implants may be sized to have a width generally as great as the nucleusportion of the disc or as wide as the area between the limit lines LL asshown in FIG. 4. There are at least two circumstances where the use ofsuch a wide implant is not desirable. Under these circumstances, the useof a pair of implants each having a width less than one half the widthof the disc space to be fused is preferred. The first circumstance iswhere the implants are for insertion into the lumbar spine from aposterior approach. Because of the presence of the dural sac within thespinal canal, the insertion of a full width implant in a neurologicallyintact patient could not be performed from a posterior approach. Thesecond circumstance is where the implants are for endoscopic, such aslaproscopic, insertion regardless of the approach as it is highlydesirable to minimize the ultimate size cross-sectionally of the path ofinsertion.

The ability to achieve spinal fusion is inter alia directly related tothe vascular surface area of contact over which the fusion can occur,the quality and the quantity of the fusion mass, and the stability ofthe construct. The overall size of interbody spinal fusion implants islimited, however, by the shape of the implants relative to the naturalanatomy of the human spine. For example, if such implants were toprotrude from the spine they might cause injury to one or more of theproximate vital structures including the large blood vessels orneurological structures.

FIG. 4 shows a top plan view of the endplate region of a vertebral bodyV with the outline of a related art implant A and implant 100 of oneembodiment of the present invention installed, one on each side of thecenterline of the vertebral body V. The length and width of related artimplant A is limited by its configuration and the vascular structuresanteriorly (in this example) adjacent to the implantation space. Thepresence of limiting corners LC on the implant precludes the surgeonfrom utilizing an implant of this configuration having both the optimalwidth and length because the implant would markedly protrude from thespine.

Related art implants also fail to maximally sit over the best structuralbone, which is located peripherally in the apophyseal rim of thevertebral body and is formed of the cortex and dense subchondral bone.The configurations of previous implants do not allow for maximizing boththe vital surface area over which fusion could occur and the areaavailable to bear the considerable loads present across the spine.Previous implant configurations do not allow for the full utilization ofthe apophyseal rim bone and the bone adjacent to it, located proximatethe perimeter of the vertebral body to support the implants at theirleading ends and to maximize the overall support area and area ofcontact for the implants. The full utilization of this dense peripheralbone would be ideal.

Therefore, there is a need for an interbody spinal fusion implant havingopposed portions for placement toward adjacent vertebral bodies that iscapable of fitting within the outer boundaries of the vertebral bodiesbetween which the implant is to be inserted and to maximize the surfacearea of contact of the implant and vertebral bone. The implant shouldachieve this purpose without interfering with the great vessels orneurological structures adjacent to the vertebrae into which the implantis to be implanted. There exists a further need for an implant that isadapted for placement more fully on the dense cortical bone proximatethe perimeter of the vertebral bodies at the implant's leading end.

SUMMARY OF THE INVENTION

The present invention relates to an artificial spinal implant formed ormanufactured prior to surgery and provided fully formed to the surgeonfor use in interbody fusion made of an implant material other than bonethat is appropriate for the intended purpose. The implant is of a widthpreferably sized to be used in pairs to generally replace all or a greatportion of all of the width of the nucleus portion of the disc. To thatend, the width of the implant is less than half of the width of the discspace. Preferably, the implant generally has parallel side walls and isused where it is desirable to insert an implant of enhanced lengthwithout the leading lateral wall protruding from the spine.

The interbody spinal implant of the present invention is for placementbetween adjacent vertebral bodies of a human spine across the height ofdisc space between those adjacent vertebral bodies. The implantpreferably does not extend beyond the outer dimensions of the twovertebral bodies adjacent that disc space, and preferably maximizes thearea of contact of the implant with the vertebral bone. In a preferredembodiment, the implant has a leading end configured to conform to theanatomic contour of at least a portion of the anterior, posterior, orlateral aspects of the vertebral bodies depending on the intendeddirection of insertion of the implant, so as to not protrude beyond thecurved contours thereof. The implant has an asymmetrical leading endmodified to allow for enhanced implant length without the corner of theleading end protruding out of the disc space. As used herein, the phrase“asymmetrical leading end” is defined as the leading end of the implantlacking symmetry from side-to-side along the transverse axis of theimplant when the leading end is viewed from a top elevation.

The configuration of the leading end of the implant of the presentinvention allows for the safe use of an implant of maximum length forthe implantation space into which it is installed. Benefits derived froma longer length implant include, but are not limited to, providing agreater surface area for contacting the vertebral bodies and forcarrying bone growth promoting material at the implant surface,increased load bearing support, increased stability, and increasedinternal volume for holding fusion promoting material and the ability tohave a portion of the implant rest upon the apophyseal rim, the beststructural bone of the vertebral endplate region. These fusion promotingand bone growth promoting materials may be bone, bone products, bonemorphogenetic proteins, mineralizing proteins, genetic materials codingfor the production of bone or any other suitable material.

The spinal implant of the present invention may also include a trailingend opposite the leading end that is configured to conform to theanatomic contour of the anterior, posterior, or lateral aspects of thevertebral bodies, depending on the direction of insertion, so as not toprotrude beyond the curved contours thereof. The present invention canbenefit interbody spinal fusion implants having spaced apart non-arcuateopposed surfaces adapted to contact and support opposed adjacentvertebral bodies as well as implants having spaced apart arcuate opposedsurfaces adapted to penetrably engage opposed vertebral bodies. As usedherein, the term “arcuate” refers to the curved configuration of theopposed upper and lower portions of the implant transverse to thelongitudinal axis of the implant along at least a portion of theimplant's length.

In one embodiment of the present invention, an implant adapted forinsertion from the posterior approach of the spine and for achievingbetter, safe filling of the posterior to anterior depth of the discspace between two adjacent vertebral bodies, and the possibility ofhaving the leading end of the implant supported by the structurallysuperior more peripheral bone including the apophyseal rim and the boneadjacent to it, includes opposed portions adapted to be oriented towardthe bone of the adjacent vertebral bodies, a leading end for insertinginto the spine, and an opposite trailing end that may be adapted tocooperatively engage a driver. In the alternative, the implant mayreceive a portion of the driver through the trailing end tocooperatively engage the implant from within and/or at the implanttrailing end. The leading end of this embodiment of the implant of thepresent invention is generally configured to conform to the naturalanatomical curvature of the perimeter of the anterior aspect of thevertebral bodies, so that when the implant is fully inserted andproperly seated within and across the disc space the implant contactsand supports a greater surface area of the vertebral bone in contactwith the implant to provide all the previously identified advantages.Moreover, at the election of the surgeon, the implant of the presentinvention is configured to be able to be seated upon the more denselycompacted bone about the periphery of the vertebral endplates forsupporting the load through the implant when installed in or across theheight of the intervertebral space.

Related art bone ring implants where the implant is a circle, oval, oroblong have trailing ends that are either modified to be squared-off, orunmodified so as to remain a portion of a circle, an oval, or an oblongand have a medial side wall that is incomplete due to a portion of themedullary canal interrupting the side wall. The present inventionimplants have an interior facing medial side wall adapted for placementmedially within the disc space with the side wall intact andsubstantially in the same plane and an exterior facing lateral side wallopposite to the medial side wall adapted for placement laterally. Theimplants of the present invention also may have a mid-longitudinal axisbetween the medial and lateral side walls wherein the mid-longitudinalaxis at the leading end extends forward further than the lateral sidewall at the leading end while the medial side wall is not equal inlength to the lateral side wall, but is greater in length.

In another embodiment of the present invention, an implant for insertionfrom the anterior approach of the spine and for achieving better fillingof the anterior to posterior depth of the disc space has a leading endgenerally configured to better conform to the natural anatomicalcurvature of the perimeter of the posterior aspect of the vertebralbodies and does not protrude laterally.

In yet another embodiment of the present invention, the implant has atrailing end that is either asymmetric or symmetric from side-to-sidealong the transverse axis of the implant. The trailing end may beadapted to conform to the anatomical contours of the anterior orposterior aspects of the vertebral bodies. For example, an implant forinsertion from the posterior or anterior approach of the spine has aleading end that is generally configured to better conform to thenatural anatomical curvature of at least one of the perimeter of theanterior and posterior aspects, respectively, of the vertebral bodiesand a trailing end that is generally configured to conform to thenatural anatomical curvature of the opposite one of the posterior andanterior aspects, respectively, of the vertebral bodies depending on theintended direction of insertion and that does not protrude laterallyfrom the vertebral bodies. When the implant is fully seated and properlyinserted within and across the disc space, the surface area of thevertebral bone in contact with the implant is more fully utilized.

As another example, an implant in accordance with the present inventionfor insertion from a translateral approach to the spine and across thetransverse width of the vertebral bodies has a leading end that isgenerally configured to better conform to the natural anatomicalcurvature of the perimeter of at least one of the lateral aspects,respectively, of the vertebral bodies. The implant also may have atrailing end that is generally configured to conform to the naturalanatomical curvature of the opposite one of the lateral aspects,respectively, of the vertebral bodies depending on the intendeddirection of insertion. Implants for insertion from a translateralapproach and methods for inserting implants from a translateral approachare disclosed in Applicant's U.S. Pat. Nos. 5,860,973 and 5,772,661,respectively, incorporated by reference herein.

The implant of the present invention is better able to sit upon thedense compacted bone about the perimeter of the vertebral bodies of thevertebral endplate region for supporting the load through the implantwhen installed in the intervertebral space. Where the spinal implant ofthe present invention is an interbody spinal fusion implant then it alsomay have at least one opening therethrough from the upper vertebral bodycontacting surface through to the lower vertebral body contactingsurface. The opening allows for communication between the opposed upperand lower vertebrae engaging surfaces to permit for growth of bone incontinuity from adjacent vertebral body to adjacent vertebral bodythrough the implant for fusion across the disc space.

For any of the embodiments of the present invention described herein,the implant preferably includes protrusions or surface roughenings forengaging the bone of the vertebral bodies adjacent to the implant. Thematerial of the implant is an artificial material such as titanium orone of its implant quality alloys, cobalt chrome, tantalum, or any othermetal appropriate for surgical implantation and use as an interbodyspinal fusion implant, or ceramic, or composite including variousplastics, carbon fiber composites, or coral, and can include artificialmaterials which are at least in part bioresorbable. The implants mayfurther include osteogenic materials such as bone morphogeneticproteins, or other chemical compounds, or genetic material coding forthe production of bone, the purpose of which is to induce or otherwiseencourage the formation of bone or fusion.

Bone for use as the base material used to form the implant isspecifically excluded from the definition of artificial materials forthe purpose of this application. Where the implants are for spinalfusion, it is appreciated that they may be adapted to receive fusionpromoting substances within them such as cancellous bone, bone derivedproducts, or others.

It is appreciated that the features of the implant of the presentinvention as described herein are applicable to various embodiments ofthe present invention including implants having non-arcuate or arcuateupper and lower opposed portions adapted to be oriented toward the boneof the adjacent vertebral bodies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a horizontal cross-section through a boneyendplate region of a vertebral body.

FIGS. 2-3 are top plan views of the fourth lumbar and first sacralvertebral bodies, respectively, in relationship to the blood vesselslocated anteriorly thereto.

FIG. 4 is a top plan plan view of an endplate region of a vertebral bodywith a prior art implant on the left side of the center line and animplant in accordance with one embodiment of the present invention onthe right side of the centerline inserted from the posterior aspect ofthe spine.

FIG. 5 is a side perspective view of the outline of an implant inaccordance with one embodiment of the present invention.

FIG. 5A is a side elevational view of an implant having a taperedleading end in accordance with an embodiment of the present invention.

FIG. 5B is a side elevational view of an implant having opposed portionsthat are generally in a converging relationship to each other from atrailing end to a leading end of the implant in accordance with anembodiment of the present invention.

FIG. 5C is a side elevational view of an implant having opposed portionsthat are generally in a diverging relationship to each other from atrailing end to a leading end of the implant in accordance with anembodiment of the present invention.

FIG. 6 is a partial enlarged fragmentary view along line 6-6 of FIG. 5.

FIG. 7 is a top plan view of a lumbar vertebral body in relationship tothe blood vessels located proximate thereto and an implant in accordancewith one embodiment of the present invention inserted from the posterioraspect of the vertebral body.

FIG. 8 is a top plan view of a lumbar vertebral body in relationship tothe blood vessels located proximate thereto and an implant in accordancewith one embodiment of the present invention inserted from the anterioraspect of the vertebral body.

FIG. 9 is a top plan view of an implant in accordance with oneembodiment of the present invention illustrating the mid-longitudinalaxis and a plane bisecting the mid-longitudinal axis along the length ofthe implant.

FIG. 10A is a top plan view of a lumbar vertebral body in relationshipto the blood vessels located proximate thereto and an implant havingarcuate upper and lower opposed portions in accordance with anembodiment of the present invention inserted from the posterior aspectof the vertebral body.

FIG. 10B is a top plan view of a lumbar vertebral body in relationshipto the blood vessels located proximate thereto and an implant havingarcuate upper and lower opposed portions in accordance with anotherembodiment of the present invention inserted from the posterior aspectof the vertebral body.

FIG. 11 is a trailing end view of a spinal implant shown in FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4 shows an embodiment of the present invention comprising aninterbody spinal implant generally referred by the numeral 100, insertedin the direction of arrow P from the posterior aspect of a vertebralbody V on one side of the centerline M in the lumbar spine. Implant 100has a leading end 102 for insertion into the disc space and an oppositetrailing end 104. In a preferred embodiment, leading end 102 isconfigured to not extend beyond the outer dimensions of the twovertebral bodies adjacent the disc space proximate leading end 102 afterimplant 100 is installed, to maximize the area of contact of the implantwith the vertebral bone. Leading end 102 could be described as beinggenerally configured to generally conform to at least a portion of thenatural anatomical curvature of the aspect of the vertebral bodiesadjacent the disc space proximate leading end 102 after implant 100 isinstalled. The general configuration of leading end 102 is furtherdescribed in connection with FIG. 9 below.

As shown in FIGS. 7 and 8, depending on the direction of insertion, forexample, when implant 100 is installed in the direction of arrow P fromthe posterior aspect of the vertebral body V, leading end 102 a isadapted to conform to at least a portion of the anterior aspect of thevertebral body V. When implant 100 is installed in the direction ofarrow A from the anterior aspect of vertebral body V, leading end 102 bis adapted to conform to at least a portion of the posterior aspect ofvertebral body V. Trailing end 104 may be symmetrical or asymmetricalfrom side-to-side along the transverse axis of the implant and canconform to at least a portion of the natural curvature of the aspect ofvertebral body V opposite to leading end 102. Trailing end 104 may ormay not be configured to conform to the aspect of vertebral body Vproximate trailing end 104 after implant 100 is installed. Trailing end104 need only have a configuration suitable for its intended use in thespine.

As shown in FIGS. 5 and 6, implant 100 has opposed portions 106 and 108that are adapted to contact and support adjacent vertebral bodies wheninserted across the intervertebral space. In this embodiment, opposedportions 106, 108 have a non-arcuate configuration transverse to thelongitudinal axis of implant 100 along at least a portion of the lengthof implant 100. Opposed portions 106, 108 are spaced apart and connectedby an interior side wall 112 and an exterior side wall 114 oppositeinterior side wall 112. Interior side wall 112 is the portion of implant100 adapted to be placed toward another implant when implant 100 isinserted in pairs into the disc space between the adjacent vertebralbodies to be fused. Interior side wall 112 is not the internal surfaceof a hollow interior of implant 100. Exterior side wall 114 is adaptedto be placed into the disc space nearer to the perimeter of thevertebral bodies than interior side wall 112. Side walls 112, 114 mayalso include at least one opening for permitting for the growth of bonetherethrough.

Preferably, each of the opposed portions 106,108 have at least oneopening 110 in communication with one another to permit for the growthof bone in continuity from adjacent vertebral body to adjacent vertebralbody and through implant 100. Implant 100 may further be hollow or atleast in part hollow. Implant 100 may also include surface rougheningson for example, at least a portion of opposed portions 106,108 forengaging the bone of the adjacent vertebral bodies.

In another preferred embodiment, the opposed portions of the implant canbe in moveable relationship to each other to allow for relative motionof the adjacent vertebral bodies after the implant is installed.

As illustrated in FIG. 9, implant 100 has a mid-longitudinal axis MLAalong its length. Mid-longitudinal axis MLA is bisected by a plane BPPperpendicular to and bisecting the length of implant 100 along themid-longitudinal axis MLA. Implant 100 has a first distance as measuredfrom point C at leading end 102 to bisecting perpendicular plane BPP atpoint E that is greater than a second distance as measured frombisecting perpendicular plane BPP at point F to the junction of leadingend 102 and exterior side wall 114 at point B. Implant 100 has a thirddistance as measured from point A at the junction of leading end 102 andinterior side wall 112 to bisecting perpendicular plane BPP at point Dthat is greater than the second distance as measured from point F topoint B. While in the preferred embodiment as shown in FIG. 9, the thirddistance from points A to D is illustrated as being longer than thefirst distance from points C to E, the third distance can be equal to orless than the first distance. In a preferred embodiment, the firstdistance measured from points C to E is greater than the second distancemeasured from points B to F; the third distance measured from points Ato D can be less than the first distance measured from points C to E;and the third distance measured from points A to D does not equal thesecond distance measured from points B to F.

In a preferred embodiment of the present invention, when implant 100 isinserted between two adjacent vertebral bodies, implant 100 is containedcompletely within the vertebral bodies so as not to protrude from thespine. Specifically, the most lateral aspect of the implanted implant atthe leading end has been relieved, foreshortened, or contoured so as toallow the remainder of the implant to be safely enlarged so as to belarger overall than the prior implants without the leading end lateralwall protruding from the disc space. Although overall enlargement of theimplant is a preferred feature of one embodiment of the presentinvention, it is not a requisite element of the invention.

While a preferred embodiment of the present invention has beenillustrated and described herein in the form of an implant havingnon-arcuate upper and lower portions along a portion of the length ofthe implant, another preferred embodiment of the present invention asbest shown in FIG. 10 includes an implant having arcuate upper and lowerportions along at least a portion of the length of the implant. All ofthe features described in association with the non-arcuate embodimentsare equally applicable to the arcuate embodiments of the presentinvention.

FIGS. 10-11 show two interbody spinal implants generally referred to bythe numeral 200, inserted in the direction of arrow P from the posterioraspect of a vertebral body V, one on either side of the centerline M inthe lumbar spine. Implant 200 is non-threaded and is configured forlinear insertion into the disc space in a direction along themid-longitudinal axis of implant 200. Implant 200 has a leading end 202for insertion into the disc space and an opposite trailing end 204. In apreferred embodiment, leading end 202 is configured to not extend beyondthe outer dimensions of the two vertebral bodies adjacent the disc spaceproximate leading end 202 after implant 200 is installed, to maximizethe area of contact of the implant with the vertebral bone. Leading end202 could be described as being generally configured to generallyconform to at least a portion of the natural anatomical curvature of theaspect of the vertebral bodies adjacent the disc space proximate leadingend 202 after implant 200 is installed. In a preferred embodiment, lessthan half of asymmetric leading end 202 is along a line perpendicular tothe mid-longitudinal axis of the implant in a plane dividing the implantinto an upper half and a lower half.

FIG. 10B shows a pair of implants 200 a′, 200 b′ having leading ends 202a′, 202 b′, respectively. The leading end configuration shown in FIG.10B is different than that shown in FIGS. 9 and 10A. Instead of thefirst distance being less than the third distance as shown in FIG. 9,FIG. 10B shows a leading end configuration where the first distance isgreater than the third distance.

In a further preferred embodiment of either arcuate or non-arcuateimplants, more than half of the leading end can be a contour that goesfrom the exterior side wall toward the mid-longitudinal axis of theimplant in the plane dividing the implant into an upper half and a lowerhalf. In another preferred embodiment of either arcuate or non-arcuateimplants, the leading end includes a curve that extends from theexterior side wall beyond the mid-longitudinal axis of the implant. Themore pronounced curve of the leading end of the implant of the presentinvention as compared to the chamfer of related art implantsadvantageously provides for closer placement of the implant's leadingend to the perimeter of the vertebral body, without the limiting cornerprotruding therefrom, to more fully utilize the dense cortical bone inthe perimeter of the vertebral bodies. The configuration of the implantof the present invention provides the use of an implant having a longeroverall length as measured from leading end to trailing end for a betterfill of the disc space. Implant 200 has opposed portions 206 and 208that are arcuate transverse to the longitudinal axis of implant 200along at least a portion of the length of implant 200 and are adapted tocontact and support adjacent vertebral bodies when inserted across theintervertebral space and into the vertebral bodies. Implant 200 canfurther include protrusions or surface roughenings such as ratchetings220 for enhancing stability. Surface roughenings may also includeridges, knurling and the like.

The present invention is not limited to use in the lumbar spine and isuseful throughout the spine. In regard to use in the cervical spine, byway of example, in addition to various blood vessels the esophagus andtrachea also should be avoided.

Further, the implant of the present invention preferably includesnon-arcuate opposed surface portions that are either generally parallelto one another along the length of the implant or in angularrelationship to each other such that the opposed surfaces are closer toeach other proximate one end of the implant than at the longitudinallyopposite other. For example, at least a portion of the opposed surfacesmay be in a diverging relationship to each other from the trailing endto the leading end for allowing angulation of the adjacent vertebralbodies relative to each other. Alternatively, at least a portion of theopposed surfaces may be generally in a converging relationship to eachother from the trailing end to the leading end for allowing angulationof the adjacent vertebral bodies relative to each other. The spinalimplant of the present invention allows for a variable surface, or anyother configuration and relationship of the opposed surfaces.

Implant 100 may be adapted to cooperatively engage a driver instrumentfor installation of the implant into the recipient site. For example, ina preferred embodiment trailing end 104 may be configured tocomplementary engage an instrument for driving implant 100.

While the exact contour and/or curvature of a particular vertebral bodymay not be known, the teaching of having the implant leading end bearcuate or truncated along one side (the lateral leading end) or fromside to side so as to eliminate the length limiting lateral leadingcorner LC or the side wall or lateral aspect junction to the implantleading end is of such benefit that minor differences do not detractfrom its utility. Further, the range of describable curvatures may bevaried proportionately with the size of the implants as well as theirintended location within the spine and direction of insertion to be mostappropriate and is easily determinable by those of ordinary skill in theart.

Generally for use in the lumbar spine, when the leading end of theimplant is a portion of a circle then the arc of radius of the curvatureof the leading end of the implant should be from 10-30 mm to be ofgreatest benefit, though it could be greater or less, and still bebeneficial. The same is true for the cervical spine where the arc ofradius is preferably 8-20 mm. While particular preferred embodiments ofthe present invention have been shown and described, it will be obviousto those skilled in the art that changes and modifications may be madewithout departing from this invention in its broader aspects.

While specific innovative features were presented in reference tospecific examples, they are just examples, and it should be understoodthat various combinations of these innovative features beyond thosespecifically shown are taught such that they may now be easilyalternatively combined and are hereby anticipated and claimed.

1. A method for installing a pair of interbody spinal implants into animplantation space formed across the height of a spinal disc space andinto vertebral bodies adjacent the spinal disc, said method comprising:providing the pair of interbody spinal implants, each of the implantsincluding: an interior facing side wall and an exterior facing side wallopposite the interior facing side wall, a leading end for insertionfirst into the disc space, the leading end being asymmetrical from sideto side and including a curved portion extending from the junction ofthe leading end and the exterior facing side wall to at least theintersection of the leading end and a mid-longitudinal axis of theimplant, a trailing end having a curved portion opposite the leadingend, a length therebetween, opposed portions between the leading andtrailing ends adapted to contact and support the adjacent vertebralbodies, the exterior facing side wall being at least in part linearalong the length, a width from the exterior facing side wall to theinterior facing side wall, and a maximum height transverse to themid-longitudinal axis and transverse to the width, the length increasingin a direction from the exterior facing side wall to the interior facingside wall along a majority of the width, the interior and exteriorfacing side walls being between the opposed portions and the leading andtrailing ends, the interior facing side wall of one implant beingadapted to be positioned adjacent the interior facing side wall of theother implant when installed into the disc space, each of the opposedportions having at least one opening therein to permit for the growth ofbone from adjacent vertebral body to adjacent vertebral body through theimplant, the interior and exterior facing side walls extending betweenthe opposed portions and having an inner surface facing each other, theopposed portions being spaced apart and the inner surfaces of theinterior and exterior facing side walls being spaced apart to define ahollow interior in communication with the openings, the implant having amaximum width as measured through the interior and exterior facing sidewalls and through the hollow interior, at least one of the implantsbeing formed at least in part of a material other than bone, thematerial comprising at least one of surgical quality titanium and itsalloys, cobalt chrome alloy, tantalum, any metal or alloy suitable forthe intended purpose, any ceramic material suitable for the intendedpurpose, and any plastic or composite material suitable for the intendedpurpose; placing at least one bone growth promoting material at least inpart into the hollow interior of the implant; inserting the pair ofimplants into the implantation space while the implants are at themaximum height; and installing the pair of implants into theimplantation space so that the implants are together in a side-by-siderelationship when in a final installed position and a majority of theleading end and at least a portion of the trailing end of each implantbetween the interior facing side wall and the mid-longitudinal axis ofeach implant is seated on and corresponds to the contour of a respectiveone of the anterior and posterior portions of the apophyseal rim bonearea of the vertebral bodies without at least a portion of the implantproximate the leading end substantially extending beyond the outerdimensions of the vertebral bodies.
 2. The method of claim 1, whereinthe providing the pair of interbody spinal implants includes providingthe pair of implants where the junction of the exterior facing side walland the leading end of each implant is adapted so as not tosubstantially extend beyond the outer dimensions of the vertebral bodieswhen inserted within the implantation space.
 3. The method of claim 2,wherein the providing the pair of interbody spinal implants includesproviding at least one of the implants having a first distance asmeasured from the leading end to a plane perpendicular to and bisectingthe length along the mid-longitudinal axis of the implant that isgreater than a second distance as measured from the perpendicular planeto the junction of the leading end and the exterior facing side wall,and a third distance as measured from the junction of the leading endand the interior facing side wall to a plane perpendicular to andbisecting the length along the mid-longitudinal axis of the implant thatis greater than the second distance.
 4. The method of claim 3, whereinthe providing step includes the sub-step of providing the implant withthe first distance being greater than the third distance.
 5. The methodof claim 3, wherein the providing the pair of interbody spinal implantsincludes providing the implant with the first distance being less thanthe third distance.
 6. The method of claim 3, wherein the providing thepair of interbody spinal implants includes providing the implant withthe first distance and the third distance being approximately equal. 7.The method of claim 3, wherein the providing the pair of interbodyspinal implants includes providing the implant with the third distancebeing substantially greater than the first distance.
 8. The method ofclaim 1, wherein the providing the pair of interbody spinal implantsincludes providing at least one of the implants with less than half ofthe leading end being along a line perpendicular to the mid-longitudinalaxis of the implant in a plane dividing the implant into an upper halfand a lower half.
 9. The method of claim 2, wherein the providing thepair of interbody spinal implants includes providing at least one of theimplants with more than half of the leading end being a contour thatgoes from the exterior facing side wall toward the mid-longitudinal axisof the implant in a plane dividing the implant into an upper half and alower half.
 10. The method of claim 2, wherein the providing the pair ofinterbody spinal implants includes providing at least one of theimplants with the leading end having a curve that extends from theexterior facing side wall beyond the mid-longitudinal axis of theimplant.
 11. The method of claim 1, wherein the providing step includesthe sub-step of providing at least one of the implants with the trailingend being adapted to conform from side to side to at least a portion ofthe peripheral contour of at least one of the anterior and posterioraspects of the vertebral bodies adjacent a disc space into which theimplant is inserted.
 12. The method of claim 1, wherein the installingthe pair of implants includes inserting the pair of implants from theposterior aspect of the vertebral bodies and the leading end of at leastone of the implants being configured to conform to the anatomic contourof at least a portion of the anterior aspect of the vertebral bodies.13. The method of claim 1, wherein the installing the pair of implantsincludes inserting the pair of implants from the anterior aspect of thevertebral bodies and the leading end of at least one of the implantsbeing configured to conform to the anatomic contour of at least aportion of the posterior aspect of the vertebral bodies.
 14. The methodof claim 1, wherein the providing the pair of interbody spinal implantsincludes providing each implant with the opposed portions being arcuate.15. The method of claim 1, wherein the providing the pair of interbodyspinal implants includes providing at least one of the implants with anoverall length sufficient to contact both the area adjacent andincluding the anterior and posterior portions of the apophyseal rimarea.
 16. The method of claim 1, further comprising combining the pairof implants with a fusion promoting substance including at least one ofbone, bone morphogenetic protein, hydroxyapatite, and genes coding forthe production of bone.
 17. The method of claim 1, wherein theinstalling the pair of implants includes engaging at least one of theimplants to a driver instrument to install the implant into theimplantation space.
 18. The method of claim 1, wherein both of theimplants have a similar composition and shape.
 19. The method of claim1, wherein the providing the pair of interbody spinal implants includesproviding at least one of the spinal implants with at least a portion ofthe opposed portions having surface roughenings.
 20. The method of claim19, wherein the surface roughenings include at least one of ratchetings,ridges, and knurling.
 21. The method of claim 1, further comprisingforming a bore across the restored height of the disc space into whichone of the implants is to be installed.
 22. The method of claim 1,wherein the installing the pair of implants includes positioning theinterior facing side wall of each implant proximate theanterior-posterior mid-line of the disc space.
 23. The method of claim1, further comprising removing bone from at least a portion of each ofthe vertebral bodies adjacent the disc space into which the pair ofimplants are adapted to be inserted to create the implantation space.24. The method of claim 23, wherein the removing bone includesdecorticating at least one of the endplates of the adjacent vertebralbodies.
 25. The method of claim 23, wherein the installing the pair ofimplants includes installing the pair of implants into the implantationspace so that the opposed portions of each implant contact each of theadjacent vertebral bodies.
 26. The method of claim 1, wherein theinstalling the pair of implants includes positioning the pair ofimplants so that the interior facing side walls of each implant contacteach other at least in part when placed side by side.
 27. The method ofclaim 1, wherein the providing the pair of interbody spinal implantsincludes providing the pair of implants that each have a width less thanone half the maximum width of the adjacent vertebral bodies into whichthe implants are adapted to be inserted.
 28. A method for installing apair of interbody spinal implants into an implantation space formedacross the height of a spinal disc space and into vertebral bodiesadjacent the spinal disc, said method comprising: providing the pair ofinterbody spinal implants, each of the implants including: an interiorfacing side wall and an exterior facing side wall opposite the interiorfacing side wall, a leading end for insertion first into the disc space,the leading end being asymmetrical from side to side and including acurved portion extending from the junction of the leading end and theexterior facing side wall to at least the intersection of the leadingend and a mid-longitudinal axis of the implant, a trailing end having acurved portion opposite the leading end and a length therebetween,opposed portions between the leading and trailing ends adapted tocontact and support the adjacent vertebral bodies, the exterior facingside wall being at least in part linear along the length, a widthbetween the interior and exterior facing side walls, and a maximumheight transverse to the mid-longitudinal axis and transverse to thewidth, the length increasing in a direction from the exterior facingside wall to the interior facing side wall along a majority of thewidth, the interior and exterior facing side walls being between theopposed portions and the leading and trailing ends, the interior facingside wall of one implant being adapted to be positioned adjacent theinterior facing side wall of the other implant when installed into thedisc space, each of the opposed portions having at least one openingtherein to permit for the growth of bone from adjacent vertebral body toadjacent vertebral body through the implant, the interior and exteriorfacing side walls extending between the opposed portions and having aninner surface facing each other, the opposed portions being spaced apartand the inner surfaces of the interior and exterior facing side wallsbeing spaced apart to define a hollow interior in communication with theopenings, the implant having a maximum width as measured through theinterior and exterior facing side walls and through the hollow interior,at least one of the implants being formed at least in part of a materialother than bone, the material comprising at least one of surgicalquality titanium and its alloys, cobalt chrome alloy, tantalum, anymetal or alloy suitable for the intended purpose, any ceramic materialsuitable for the intended purpose, and any plastic or composite materialsuitable for the intended purpose, at least one of the implants having adistance along the mid-longitudinal axis as measured from the leadingend to a plane perpendicular to and bisecting the length along themid-longitudinal axis of the implant, a majority of the leading end ofthe at least one implant being a distance from the perpendicular planethat is less than the distance along the mid-longitudinal axis from theleading end to the perpendicular plane; placing at least one bone growthpromoting material at least in part into the hollow interior of theimplant; inserting the pair of implants into the implantation spacewhile the implants are at the maximum height; and installing the pair ofimplants into the implantation space so that the implants are togetherin a side-by-side relationship when in a final installed position and amajority of the leading end and at least a portion of the trailing endof each implant between the interior facing side wall and themid-longitudinal axis of each implant is seated on and corresponds tothe contour of a respective one of the anterior and posterior portionsof the apophyseal rim bone area of the vertebral bodies without at leasta portion of the implant proximate the leading end substantiallyextending beyond the outer dimensions of the vertebral bodies.
 29. Themethod of claim 28, wherein the providing the pair of interbody spinalimplants includes providing at least one of the implants with more thanhalf of the leading end being a contour that goes from the exteriorfacing side wall toward the mid-longitudinal axis of the implant in aplane dividing the implant into an upper half and a lower half.
 30. Themethod of claim 28, wherein the providing the pair of interbody spinalimplants includes providing at least one of the implants with theleading end having a curve that extends from the exterior facing sidewall beyond the mid-longitudinal axis of the implant.
 31. The method ofclaim 28, wherein the providing the pair of interbody spinal implantsincludes providing each implant with the opposed portions being arcuate.32. The method of claim 28, further comprising combining the pair ofimplants with a fusion promoting substance including at least one ofbone, bone morphogenetic protein, hydroxyapatite, and genes coding forthe production of bone.
 33. The method of claim 28, wherein theproviding the pair of interbody spinal implants includes providing atleast one of the spinal implants with at least a portion of the opposedportions having surface roughenings.
 34. The method of claim 33, whereinthe surface roughenings include at least one of ratchetings, ridges, andknurling.